The present invention relates to an X-ray computed tomography (CT) apparatus for medical use or industrial use, or more particularly, to speed-up in image reconstruction and improvement in image quality for a conventional (axial) scan, a cine scan, or a helical scan.
In X-ray CT apparatuses including a two-dimensional X-ray area detector that is represented by a multi-array X-ray detector or a flat-panel detector and that has a matrix structure, two methods described in FIG. 6 are conceivable as methods for reconstructing an image of a slice thickness that is larger than the width of one detector array included in the multi-array X-ray detector (refer to, for example, Patent Documents 1 and 2). One of the methods is a z-direction filter convolution method (hereinafter, which may be referred to as projection data z-direction filtering) that manipulates projection data, and the other is z-direction filtering that manipulates image space data (hereinafter, which may be referred to as image space z-direction filtering). These methods have the advantage and disadvantage described in FIG. 6.
The above image reconstruction methods for the X-ray CT apparatus have an advantage and a disadvantage, and pose a problem in terms of speed-up in image reconstruction and image quality.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-73360
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2004-230030
However, in the above X-ray CT apparatus, as the conical angle of an X-ray cone beam is getting larger, various image reconstruction algorithms are devised. Consequently, the freedom in controlling a slice thickness has increased. On the other hand, an image reconstruction time and image quality relate to each other as trade-offs and are tend to be optimized.